1. Field
The present embodiments generally relate to systems and methods for cooling and solidifying asphaltenes.
2. Description of the Related Art
Heavy hydrocarbons, such as high molecular weight, viscous, non-Newtonian fluids are produced during extraction and refining processes. Such heavy hydrocarbons typically require upgrading prior to transport. Often, one or more solvents such as diesel fuel are used to reduce the viscosity and improve the pumpability and facilitate the transport of heavy hydrocarbons. Alternatively, heavy hydrocarbons can be deasphalted using one or more deasphalting processes such as the Residuum Oil Supercritical Extraction (“ROSE®”) treatment process. Using the ROSE treatment process, the heavy hydrocarbons are introduced to a solvent extraction process wherein high viscosity asphaltenes and resins (“asphaltenic hydrocarbons”) are separated and removed, providing a low viscosity deasphalted oil. Similar asphaltenic hydrocarbons can be generated during heavy hydrocarbon refining processes. While generated using two different processes, i.e. solvent extraction and/or refining, the asphaltenic hydrocarbons share similar characteristics. Both are heavy molecular weight hydrocarbons, which at ambient temperatures are solid or semi-solid, both require elevated temperatures to maintain pumpability, and both require upgrading to provide one or more fungible products.
Where local upgrading facilities are unavailable or capacity limited, the asphaltenic hydrocarbons must be transported via truck, rail, or pipeline to one or more remote upgrading facilities. Asphaltenic hydrocarbons are often maintained at elevated temperatures to permit loading and unloading of the liquid or semi-solid asphaltenic hydrocarbons to/from truck, rail, and/or pipeline. The need to maintain the asphaltenic hydrocarbons at elevated temperatures throughout transport increases cost, complicates the process, and risks solidification of the asphaltenic hydrocarbons should the temperature decrease to a temperature at which the asphaltenic hydrocarbons solidify. Solidified asphaltenic hydrocarbons can plug pipelines and require extensive maintenance and/or cleaning of pipelines, trucks, and rail transport wagons. As an alternative to fluid or semi-solid transport, the asphaltenic hydrocarbons can be cooled in bulk and solidified prior to transport. However, bulk solidification, loading, transport, and unloading of bulk solidified materials can be cost, labor, and maintenance intensive.
To minimize special equipment and/or handling requirements, the asphaltenic hydrocarbons can alternatively be solidified into smaller particles or pellets prior to transport. Various methods for pelletizing heavy hydrocarbons have been developed. For example, U.S. Pat. No. 7,101,499 describes a process where molten heavy hydrocarbons can be formed into a series of drops which fall into a bath of coolant beneath the hydrocarbon distributor. Alternatively, U.S. Pat. Nos. 6,331,245, 6,361,682, and 6,499,979 describe one or more wetted pelletizers which provide relatively uniform heavy hydrocarbon solids by “spraying” a molten asphaltenic hydrocarbon through a rotary head to form a plurality of hydrocarbon droplets. The individual hydrocarbon droplets forming the “spray” can “skin” over while in flight, solidifying into hydrocarbon pellets as they impact and flow down the walls of the wetted pelletizer into an underlying cooling fluid bath. The usefulness of the cooling bath or the wetted pelletizer is limited, however, based upon the variable specific gravity of the hydrocarbon pellets, which can range from less than water (i.e. a specific gravity of less than 1.0 or an API density of greater than 10°) to greater than water (i.e. a specific gravity of greater than 1.0 or an API density of less than 10°). The formation of both floating and sinking hydrocarbon pellets within the cooling fluid reservoir makes the separation and removal of the pellets difficult since the floating pellets tend to agglomerate forming large masses, which are not amenable to removal from the cooling fluid reservoir particularly where the reservoir is located within an enclosed vessel.
There is a need therefore, for improved systems and methods for pelletizing heavy hydrocarbons.